The present invention relates to a method for purifying epidaunorubicin, in particular to the separation of epidaunorubicin and epi-feudomycin, which is formed as a by-product in the biotechnological production of epidaunorubicin.
Epidaunorubicin is a 4′-epimer of daunorubicin, which is in the group of glycosides and represents an antibiotic of the group anthracyclines. It is mainly used as a precursor to epirubicin which is used as a cytostatic in chemotherapy of breast cancer, non-Hodgkin lymphoma, sarcoma, stomach carcinoma and other solid types of cancer. Epidaunorubicin can be produced synthetically, semi-synthetically and biotechnologically. In the biotechnological production, various Streptomyces peucetius strains are used. Epidaunorubicin can be represented by the following general formula (I):

In the microbial synthesis of the epidaunorubicin, the problem arises that in addition to the desired product, epi-feudomycin, inter alia, is formed as a by-product which, due to its structural similarity, is very hard to separate from the epidaunorubicin. The presence of the by-product is detrimental to the yield and degree of purity of the epirubicin which is formed from the epidaunorubicin in a subsequent process step. Usually, the separation and purification of the epidaunorubicin from the fermentation broth is carried out by means of liquid-liquid extraction, chromatography and crystallization.
However, due to the presence of the epi-feudomycin, this requires a complicated process and results in a relatively high loss of epidaunorubicin.
EP 1 990 405 A1 describes different microbial strains which are suitable for the biotechnological production of epidaunorubicin. The separation of the epidaunorubicin from the fermentation broth is carried out via extraction with chloroform at an alkaline pH value. The resulting raw mixture is then further purified chromatographically with chloroform as the mobile phase. In a last step, the epidaunorubicin is crystallized by the addition of butanol and the adjustment of an acidic pH value.
EP 2 301 943 B1 describes the crystallization of epidaunorubicin hydrochloride from a mixture of alcohol/chloroform, whereby the alcohol is added at a temperature of 60° C.
EP 0 030 295 B1 discloses the synthetic production of epidaunorubicin.
WO 2010/028667 describes the extraction of 13-DHED, epidaunorubicin and epi-feudomycin from a fermentation broth with the aid of an adsorbing resin.
EP 2 042 608 B1 describes the extraction of aglycones from a fermentation broth containing 13-DHED, epidaunorubicin and feudomycin. The glycosides are extracted from the aqueous phase by means of chloroform at a slightly alkaline pH value. The pH value is kept stable by means of a saturated NaHCO3 solution.
The common methods for purifying epidaunorubicin from a fermentation broth are associated with high technical and financial expenses. The separation of epidaunorubicin and epi-feudomycin, in particular, is especially difficult due to the structural similarity of the two compounds so that an acceptable degree of purity of the epidaunorubicin can only be achieved in conjunction with a considerable yield loss. Due to the difficult separation of the epi-feudomycin, this impurity can also be found in the products derived from the epidaunorubicin, which is particularly disruptive for the conversion to epirubicin. On the other hand, a high degree of purity and a high yield are especially crucial for the subsequent conversion from epidaunorubicin to epirubicin.
Therefore, there is a need for a process which allows for an effective separation of the by-product epi-feudomycin from the desired product epidaunorubicin, without significantly lowering the yield of epidaunorubicin due to the separation and purification steps.